1. Field
The embodiments discussed herein are related to a virtualization switch and a method for controlling a virtualization switch.
2. Description of the Related Art
In a computer system using a plurality of storage apparatuses, virtualization of a storage can cause a host computer to recognize a storage area obtained by combining storage areas of a plurality of physical storage apparatuses as a virtual storage apparatus.
For example, as shown in FIG. 6, a plurality of host computers (node apparatuses) 1 and a plurality of physical storage apparatuses 2 are connected to each other by fibre channels through a fibre channel switch (network switch) 3, and some or all the storage areas in the plurality of physical storage apparatuses 2 are combined to each other by a network processor 4 of the fibre channel switch 3 to configure an apparatus as a virtual storage apparatus (virtual sharing disk) 5. A computer system can provide the virtual storage apparatus 5 to the host computers 1 such that the host computers 1 can access the virtual storage apparatus 5 is known (for example, see Japanese Patent Application Laid-Open No. 2003-44421).
According to the virtualization of the storage by the fibre channel switch, a user can freely structure a virtual storage apparatus suitable for a host computer. The host computer accesses the virtual storage apparatus to make it possible to use a physical storage apparatus without regarding storage capacities, connection conformations, and the like of the physical storage apparatuses.
Furthermore, in the virtualization of the storage using the fibre channel switch, a plurality of fibre channel switches are multiplexed to set redundant paths to provide a configuration which improves reliability (for example, see Japanese Patent Application Laid-Open No. 2007-172172).
As illustrated in FIG. 7 a computer system can have a configuration in which a plurality of fibre channel switches are multiplexed to set redundant paths.
In FIG. 7, one host computer 11 is connected to two fibre channel switches 10a and 10b by a fibre channel (FC).
The two fibre channel switches 10a and 10b are connected to a RAID (Redundant Arrays of Inexpensive Disks) storage apparatus 14 by a fibre channel (FC). As the RAID storage apparatus 14, a plurality of physical storage apparatus are virtually configured as one storage apparatus.
The two fibre channel switches 10a and 10b are connected to two hubs 12a and 12b by an Ethernet (R) serving as an example of a LAN communication standard, respectively.
Furthermore, the hubs 12a and 12b are connected to a manager computer 18 by an Ethernet Et, respectively. The manager computer 18 executes management such that virtual volumes or the like in the fibre channel switches 10a and 10b are set through the hubs 12a and 12b. 
The two fibre channel switches 10a and 10b are connected not only by a connection by the Ethernet through the hubs 12a and 12b but also by a fibre channel.
The fibre channel switches 10a and 10b cause the host computer 11 to recognize virtual storage apparatuses having the same configuration. The host computer 11 can similarly access the virtual storage apparatus through any one of the two fibre channel switches 10a and 10b. 
When the redundant system configuration is employed, even though, for example, a problem of breakdown of any one of the fibre channel switches 10a and 10b is posed, a system operation can be continued. Resistance to system failure can be improved.
A countermeasure against occurrence of a failure in the system will be described with reference to FIG. 8. An example in which only one hub is arranged to simplify the description will be described.
Any one of a plurality of fibre channel switches is set as a main switch (may be called a master switch as a general term in this specification), and the other is set as a sub-switch (may be called a slave switch as a general term). In this example, the two fibre channel switches are used, the left fibre channel and the right fibre channel being set as master and slave fibre channels, respectively.
In the fibre channel switches 10a and 10b, abnormal communication of an Ethernet can be detected through the Ethernet and the hub 12.
When any one of the fibre channel switches 10a and 10b detects abnormal communication of the Ethernet, the fibre channel switch 10a on the master side executes a failover process which takes over the process on the slave side. The fibre channel switch 10a on the master side outputs a closing designation command to perform a closing process to the fibre channel switch 10b on the slave side.
On the other hand, the fibre channel switch 10b on the slave side receives the closing designation command to close the access between the host computer 11 and the RAID storage apparatus 14.
Conventionally, in a computer system when the Ethernet communication between fibre channel switches is abnormal, the failover process is always executed on the master side, and the process is continued by the switch on one side.
However, when two Ethernets are connected between each of the fibre channel switches and the hub, even though the abnormal communication of the Ethernet can be detected, a specific line on which the abnormal communication occurs is not determined. Therefore, in the conventional configuration which always performs the failover process on the master side, even though a failure occurs in the Ethernet between the fibre channel switch on the master side and the hub, the slave side has been closed. For this reason, the system may go down disadvantageously.